Many types of memory elements for digital electronic signals have been commercially available for many years. One type is a ferrite core memory in the form of ferrite rings in single aperture core memories. Another type is in the form of magnetic domains in magnetic bubble memories. Yet another type of memory device is in the form of bi-stable multivibrator in a random access memory (RAM) with a buffer battery to compensate for electrical power failures. Still another type of memory device is in the form of capacitors capable of being charged and discharged within an electrically erasable programmable read only memory (EEPROM).
The EEPROM generally has a slow response and has undergone development as disclosed in an article in "Electronics Week", Mar. 11, 1985 starting at page 69. From this article, it appears that a memory of this type is provided with a few thousand memory elements for most applications. The article also indicates that one can install a power supply producing an operating voltage of about 25 volts for the memory device on the same semiconductor substrate next to the memory elements, the controller and the read-out circuit. The operative voltage of 25 volts is considerably higher than the supply voltage for the semiconductor substrate which is ordinarily about +5 volts.
A description of the elements and the organization of semiconductor memories in general is disclosed in many books such as the book entitled, "MOS Device and Circuit Design", by Oliver J. McCarthy, published by John Wiley & Sons, 1983.
The prior art memory devices have many disadvantages. Ferrite core memories and magnetic bubble memories cannot be manufactured by the same technological methods used for control circuits and are relatively slow and expensive. Semiconductor memories store information only for a limited time such as until the battery on a RAM is exhausted or until the charge has dissipated out of the capacitor of an EEPROM memory cell. The charge in an EEPROM memory cell can be dissipated under the influence of ionizing radiation. The EEPROM memory cell is also limited in the number of writing cycles, typically from 10.sup.4 to 10.sup.6.
A memory device in the form of a micro-mechanical device is an alternative memory element for storing digital electronic signals. Micro-mechanical devices, particularly electrical switches of microscopic dimensions, can be fabricated on a semiconductor substrate such as silicon. The same manufacturing steps used to fabricate electronic elements in an integrated circuit can be used. These include manufacturing steps such as diffusion, oxidation, fabrication of thin layers, masking, etching, and photolithographic techniques. U.S. Pat. No. 4,570,139 and the references cited therein generally show the state of the art for the fabrication of micro-mechanical devices.